Peripheral membrane component of the cis-Golgi stack that acts as a membrane skeleton that maintains the structure of the Golgi apparatus,and as a vesicle thether that facilitates vesicle fusion to the Golgi membrane. Required for normal protein transport from the endoplasmicreticulum to the Golgi apparatus and the cell membrane. Together with p115/USO1 and STX5, involved in vesicle tethering and fusion at thecis-Golgi membrane to maintain the stacked and inter-connected structure of the Golgi apparatus. Plays a central role in mitotic Golgidisassembly: phosphorylation at Ser-37 by CDK1 at the onset of mitosis inhibits the interaction with p115/USO1, preventing tethering of COPIvesicles and thereby inhibiting transport through the Golgi apparatus during mitosis. Also plays a key role in spindle pole assembly andcentrosome organization.
